The present disclosure relates to a photovoltaic device useful for generating an electrical current upon exposure to wide spectrum light, such as sunlight. The materials described herein can be used in organic solar cells.
A photovoltaic device typically contains a layer of a photoactive material (i.e. an active layer) sandwiched between two electrodes (i.e. a cathode and an anode). The photoactive layer can absorb the energy in a photon emitted by radiation, such as sunlight. This photon energy creates an exciton, or bound electron-hole pair. Depending on the material, the electron and hole can travel a short distance (on the order of tens of nanometers) before spontaneous recombination occurs. The exciton can move to a junction where they can be separated, so that electrons are collected at one electrode and holes are collected at the other electrode. This allows current to flow through an external circuit.
Most organic/polymeric semiconductor materials used in solar cell applications have limited storage life, making their implementation difficult. For example, poly(3-hexylthiophene), the best known material in plastic solar cells, has a storage life of only about 1 year. Most organic solar active materials also require post-coating thermal and/or vacuum treatments, as well as additional buffer or blocking layers in their structure, to prevent leakage or facilitate photovoltaic effects. These factors make the fabrication process very cumbersome.
It would be desirable to develop new photovoltaic devices that can achieve a longer storage life and can be fabricated in an ambient environment without any post-casting treatments or any buffer or blocking layers. It would also be desirable to provide a photovoltaic device that can capture more of the light energy present in sunlight and generate greater amounts of electricity, increasing the power conversion efficiency of the device.